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APES Chapter 6 Review Guide
Transcript of APES Chapter 6 Review Guide
Nature Exists at Several Levels of Complexity
There are many different levels of nature and ecosystems to consider when looking at environments. We can also group certain areas into biomes based on their similarities in temperature and precipitation as well as some other features that might define a biome.
Growth Models Help Ecologists Understand Population Changes
Population ecologists use growth models as a tool that incorporates density-dependent and density-independent factors in order to predict and find changes that may occur in a population.
Community Ecologists Study Species Interaction
The study of the interactions that determine an individual's survival in a habitat is called community ecology.
The Composition of a Community Changes Over Time
Ecological succession is the predictable replacement of one group of species by another group of species over time. It is also important to note that changes in nature occur without human activity and are happening constantly.
There are five main characteristics of populations:
Population Size: This is the total number of individuals within the population (a given area in a given time period).
Population Density: This is the number of individuals per given unit of area of the population.
Population Distribution: This is a description of how the individuals of a population are distributed throughout the area and can be defined as random distribution, uniform distribution, or clumbed distribution.
Population Sex Ratio: This is the ratio of males to females in the population.
Population Age Structure: This is the description of how many individuals of a population fit into particular age categories.
Factors that Influence Population Size
The largest factor that influences population size is a limiting resource. These are resources of any kind that the population needs to survive, and the population can increase with the introduction of more of this limiting factor. Carrying capacity is also a big factor that influences population size, because it is the maximum size of a population that an environment can support. To be more broad, density-dependent factors are factors that may affect population size, but the magnitude of the effect is impacted by the size of the population. Likewise, density-independent factors are factors that affect population size, but the magnitude of the affect IS DEPENDENT on the size of the population.
Population Ecologists Study the Factors that Regulate Population Abundance and Distribution
Populations can be described as dynamic and constantly changing.
"The study of factors that cause populations to increase or decrease is the science of population ecology." P. 151
The knowledge of factors that regulate populations can be crucial to helping us maintain and recuperate endangered species and keep our earth alive.
The Logistic Growth Model
This model describes a population that increases exponentially, and then steadies as the population reaches carrying capacity. The graph makes an S-shaped curve under logistic growth.
Variations on the Logistic Growth Model
Overshoot is a phenomenon that occurs in a population when the population exceeds the carrying capacity of its environment. Die-off is a product of a population exceeding the carrying capacity where the population crashes. Many populations undergo population oscillations or cycles that represent the population overshooting and dying off in a cycle. Factors that can keep population in check can be things such as disease and predators as well. As predators prey on a population, it may decline as the predator population increases, and as there are less prey available the predator population may decline as the prey population shoots up again in a cycle.
The Exponential Growth Model
Growth Rate is the number of births minus the number of deaths of individuals within a population. The maximum potential growth rate is called the intrinsic growth rate and is denoted as "r". The exponential growth model of a population is graphed using:
Exponentrial growth makes a J-shaped curve because the numbers increase exponentially thus increasing the slope of the graph.
A group of populations that are separated spatially and only connected through some movements of individuals between the populations is called a metapopulation. These populations are connected through corridors, or strips of habitat that might connect populations.
Reproductive Strategies and Survivorship Curves
There are two different types of strategies that species have for growth. The K-selected species have low intrinsic growth rates, they slowly and steadily reach carrying capacity of their environment. Then there are also R-selected species that have higher intrinsic growth rates and can often lead to overshooting and die-off within the population. The graph below shows survivorship curves of some species. These are plotted graphs of survivors within populations of different species that show the population and the age of individuals within the population as well as a general pattern within different types of species. Species in a type 1 survivorship curve are generally K-selected, and species in a type 3 survivorship curve are generally R-selected. A constant decline in survivorship as a species ages would match a type 2 curve.
Competition can be described as the struggle of individuals to obtain a certain resource. It is also important to know the competitive exclusion principle that states that:
Two species competing for the same limiting resource cannot coexist.
Resource partitioning is the act of species dividing a resource based on morphology or behavior so that they MAY coexist.
There are three main types of resource partitioning split into temporal resource partitional, having to do with time, spatial resource partitioning, having to do with space, and morphilogical resource partitioning, having to do with the morphology of the species and how they interact with the resource due to their morphology.
Predation is the use of one species as a resource of another species. Predators are split into four real categories: true predators, herbivores, parasites, and parasitoids. True predators include relationships such as lions and gazelle, while herbivores are individuals that consume plants as prey. Parasites are individuals that live on their host, and only consume a fraction of their host and rarely causes death. Parasites that inflict disease on their host are called pathogens and are more dangerous. Parasitoids are individuals that lay their eggs inside other organisms and most of the time eventually kill the host, which is terrible. Along with predators, there are predator defenses that their prey may acquire through evolution that defend against predators such as a poison dart frog's toxic skin.
Mutualism can be any set of interactions between organisms that is be beneficial to the survivorship of both organisms. An example might be between the crocodiles of the nile and the egyptian plover bird where the plover bird gets a meal by cleaning the crocodile's teeth.
Commensalism is a relationship where neither individual is harmed or benitted such as birds using trees for perches. It is also important to note that a symbiotic relationship is a relationship between two species that live within close association with one another.
A keystone species is a species that plays a role much larger than what its relative abundance might suggest. This name derives from the keystone of an arch, without it the arch would collapse. Some keystone species are considered instrumental because they provide mutualistic services to members of another species. Keystone species may also be ecosystem engineers, which are species that maintain or create an environment for other species.
Predator mediated competition is competition in which the predator is essential in in reducing the abundance of a superior competitor in the environment and allowing other competitors to exist. This is important in maintaining a healthy environment and biodiversity.
Primary succession occurs on areas such as newly cooled lava or parking lots that are barren and void of soil. The picture below goes through the primary succession process as the lichens and mosses die off and mix with the eroded rock from the ground to produce soil.
Secondary Succession occurs in areas that have been disturbed such as in a hurricane or tornado, but have yet to lose their soil. Pioneer species are species that can colonize and revitalize new areas such as these because of their ability to grow rapidly and grow well in full sunlight such as these areas.
Aquatic succession can occur in the medium of high tide, or even over thousands of years by sediment and vegetation making lakes increasingly shallow.
The Species Richness of a Community is Influenced by Many Factors
The Number and type of species in a given area are dependent on colonization, speciation, and extinction losses of species from the area. These factors are affected by another set of factors.
Habitat Size and Distance: The Theory of Island Biogeography
The theory of island biogeography is simpily a theory that tells how habitat size and distance from other habitats can be a factor of species richness. It has to do with a group of islands that were observed and how larger islands that were closer to the continent had more species richness than the smaller and farther off islands.
Conservation and Island Biogeography
In basic terms, if we want to be conservative with our environment and keep areas in high levels of species richness, we need to consider these factors.
The fact that latitude affects the amount of species and types of species in an area is certain. The reasoning behind it, however is not. Scientists are boggled by why this pattern occurs. between all sorts of individuals.
Time is also an important factor because the longer an environment exists, the more time there has been for speciation and extinction to occur. This can result in more developed levels of biodiversity.